1. Field of the Invention
The present invention relates to an X-ray detection system and, more particularly, to an X-ray detection system which, when it is attached to a scanning electron microscope and soft X-rays are spectroscopically analyzed, is able to measure a wide energy range.
2. Description of the Related Art
When a charged-particle beam such as an electron beam is directed at a sample, characteristic X-rays are emitted from the sample. The characteristic X-rays are detected by a detector, and the composition of the sample is measured. This technique is known as energy dispersive X-ray spectroscopy and makes use of the phenomenon that characteristic X-rays have energies intrinsic to elements constituting the sample. The number of X-rays produced per unit time is counted for each energy of the X-rays and thus information about the constituent elements of the sample is obtained. Usually, a semiconductor detection device using a semiconductor crystal such as silicon or germanium is used as a means for detecting X-rays.
On the other hand, there exists an imaging technique. In particular, a sample is irradiated with a charged-particle beam such as an electron beam. The resulting characteristic X-rays are made to impinge on a diffraction grating. As a result, diffracted X-rays are separated. The diffracted X-rays are detected by an X-ray CCD image sensor, whereby the X-rays are imaged.
An instrument for implementing this technique is designed including an electron beam irradiation portion for irradiating a sample with an electron beam, a diffraction grating with unequal pitch (varied line-space (VLS) diffraction grating), an X-ray focusing mirror for focusing the characteristic X-rays emitted from the irradiated sample and directing the X-rays toward the grating which receives the focused characteristic X-rays and produces diffracted X-rays, and an image sensor (back-illuminated CCD camera) for detecting the diffracted X-rays.
An X-ray detection system of this type is also described in patent document 1 (described below).